A large variety of molecular sieves have been disclosed in the art as useful in catalysts for hydrocarbon conversion. The most well known are the crystalline aluminosilicate zeolites formed from corner-sharing AlO.sub.2 and SiO.sub.2 tetrahedra. The zeolites generally feature pore openings of uniform dimensions, significant ion-exchange capacity and the capability of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without displacing any atoms which make up the permanent crystal structure. Zeolites often are characterized by a critical, usually minimum, silica/alumina ratio.
More recently, a class of useful non-zeolitic molecular sieves containing framework tetrahedral units (TO.sub.2) of aluminum (AlO.sub.2), phosphorus (PO.sub.2) and at least one additional element EL (ELO.sub.2) has been disclosed as being useful in hydrocarbon conversion. "Non-zeolitic molecular sieves" include the "ELAPSO" molecular sieves as disclosed in U.S. Pat. No. 4,793,984 (Lok et al.), "SAPO" molecular sieves of U.S. Pat. No. 4,440,871 (Lok et al.) and crystalline metal aluminophosphates--MeAPOs where "Me" is at least one of Mg, Mn, Co and Zn--as disclosed in U.S. Pat. No. 4,567,029 (Wilson et al). Framework As, Be, B, Cr, Fe, Ga, Ge, Li, Ti or V and binary metal aluminophosphates are disclosed in various species patents. Particularly relevant to the present catalyst is U.S. Pat. No. 4,758,419 (Lok et al.), which discloses MgAPSO non-zeolitic molecular sieves. Generally the above patents teach a wide range of framework metal concentrations, e.g., the mole fraction of (magnesium+silicon) in Lok et al. '419 may be between 0.02 and 0.98 with a preferable upper limit of 0.35 mole fraction and magnesium concentration of at least 0.01, for sieves useful in hydrocarbon conversion.
The catalytic alkylation of aromatics with olefins is practiced commercially to yield such petrochemical intermediates as ethylbenzene, cumene, and linear alkylbenzenes. Such monoalkylaromatic compounds are important chemical precursors in the production of resins, surface-active agents, and other products. Polyalkylaromatic compounds such as diethylbenzene and diisopropylbenzene are lower-volume commercial products.
Known aromatic-olefin alkylation catalysts include Friedel-Crafts catalysts in either liquid or solid supported form, e.g., sulfuric acid, phosphoric acid, hydrofluoric acid, and aluminum chloride. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized in alkylation catalysts. A transalkylation reaction zone may be added to an alkylation zone to enable higher alkylation conversion through reaction of the resulting undesired polyalkylaromatics into desired monoalkylaromatic compounds. The transalkylation catalyst may be the same or a different composition than the alkylation catalyst. The alkylation may be effected in a variety of processing schemes employing one or more of an alkylation reaction zone, a transalkylation reaction zone, and a separations zone, with various product, feed, and intermediate-product recycles known to produce monoalkylaromatic products in high yields.
A drawback inherent to some alkylation/transalkylation processes using Friedel-Crafts catalysts such as solid phosphoric acid or hydrofluoric acid catalysts results from a water cofeed and resulting production of an extremely corrosive sludge by-product. The utilization of such sludge-producing catalysts in an alkylation process requires that costly special design provisions be made regarding unit metallurgy, safety, and by-product neutralization. The use of Friedel-Crafts catalysts additionally dictates a once-through processing scheme to ensure that damaging corrosive materials are not recycled into the reaction zone, necessitating operation of the process at high conversion with resulting greater amounts of unwanted byproducts such as alkylating agent oligomers and heavy alkylate.
Problems relating to the Friedel-Crafts catalysts were addressed by development of catalysts containing a zeolitic molecular sieve for the alkylation of aromatics, for example as disclosed in U.S. Pat. No. 3,751,504 (Keown et al.). Incorporation of magnesium into a zeolite for disproportionation of aromatics is disclosed in U.S. Pat. No. 4,034,053 (Kaeding et al.). Alkylation of an aromatic and an olefin using a crystalline magnesium silicate catalyst in which the magnesium is incorporated into the crystalline structure during its formation is disclosed in U.S. Pat. No. 4,721,827 (Cullo et al.). The use of a catalyst containing a MgAPSO non-zeolitic molecular sieve in hydrocarbon conversion including alkylation is disclosed in the aforementioned U.S. Pat. No. 4,758,419 (Lok et al.).
An ongoing issue facing workers in the aromatic-olefin alkylation field is how to reduce such process byproducts such as olefin oligomers, heavy polyaromatic compounds, and unwanted monoalkylaromatics. Olefin oligomers are troublesome in that they often are recovered with the desired monoalkylaromatic product where they can detrimentally affect the utility of this intermediate in further conversion processes. An example of this would be the contamination of cumene with propylene oligomers which may reduce the utility of such contaminated cumene as a phenol process feedstock and ultimately for the production of phenolic resins due to the presence of the oligomers as an inert compound within the cross-linked resins. An example of unwanted monoaromatics is n-propyl benzene in cumene production, which is poorly converted in the phenol process and results in a yield loss through cumene purge and contamination of the acetone byproduct with impurities.